1. Field of the Invention
The present invention relates to a method of evaluating silica powder, a vitreous silica crucible, and a method of manufacturing a vitreous silica crucible.
2. Description of the Related Art
A vitreous silica crucible used for pulling a silicon single crystal can be manufactured by the processes of (1) forming a silica powder layer by depositing, in a predetermined thickness, crystalline or amorphous silica powder on the inner surface (the bottom surface and the side surface) of a rotating mold having an bowl-shaped inner surface defining the outer shape of the vitreous silica, while rotating the mold, and (2) vitrifying the silica powder layer by heating and fusing the silica powder layer up to a temperature of 2000 to 2600 deg. C. by use of arc discharge, followed by cooling.
In pulling a silicon single crystal, the vitreous silica crucible is heated up to a temperature equal to or higher than the melting point of silicon (1420 deg. C.). When vitreous silica is heated up to such temperature, a portion of the vitreous silica is crystallized. Crystallized portion is easily peeled off. When the peeled-off crystal pieces drop and mix in silicon melt retained in the crucible, the crystal pieces are carried to a silicon single crystal by way of heat convection and so on. As a result, the pulled ingot is crystallized, and the single crystallization yield of the ingot deteriorates.